1. Field of the Invention
Multiple branch wells used to inject and recover a leach solution and minerals from the same common casing.
2. Description of the Prior Art
Multiple branch wells from a common generally vertical main casing are disclosed in the prior in situ leach mining art as evidenced by the U.S. Pat. No. 4,222,611 and 4,249,777, both to W. C. Larson et al and assigned to the same assignee as herein. The former invention is of particular relevancy to this invention. However, many of the specific methods used to form the branch wells of the preferred embodiment of this invention are not disclosed in these two earlier patents. The methods can be found in a copending U.S. patent application Ser. No. 276,551 filed June 23, 1981, entitled "Multiple Branch Completion with Common Drilling and Casing Template" by the same inventive entity as here. The contents of this last mentioned invention and what is being disclosed and claimed here, as well as other related inventions, were first publically disclosed on Jan. 18-22, 1981, at the ASME Petroleum Division Meeting in Houston, Tex. A handout thereat entitled "Drilling and Completing Multiple Branched Boreholes" is incorporated by reference herein. All of the work described in this handout was done under a contract between the U.S. Department of the Interior, Bureau of Mines, and Maurer Engineering Inc., of Houston, Tex. The final contract report dated July 1980 was first released to the public by the U.S. Bureau of Mines in January 1981.
The closest known prior art to what is being disclosed and claimed herein is the mentioned U.S. Pat. No. 4,222,611. Therein two branch wells are whipstocked from a hole to form a combined injection and recovery main generally vertical well. One or both of these branch wells serve as injector wells and the main well serves as the recovery or producer well. At the lower end of the main well a conduit and pump are inserted to allow the leach solution with its mineral bearing material to be recovered to the surface. As disclosed in this patent (column 2, lines 56-66), a hollow drop pipe 15 with an electrically operated submersible pump 17 extends near or into the ore zone to provide for the recovery. This invention is an improvement of that previous lift system. Herein we utilize the fluid injected from pump on the surface as the source of power for a retrievable downhole hydraulically operated positive displacement pump. This has many advantages over the electrically operated submersible pump which is fixed in its casing. It conserves casing cross-sectional space by putting pump in tandem with injection tubing, thus allowing injection or production from a single well head. The pump is wireline retrievable to allow surface repairs and/or maintenance to take place. Less surface plumbing is required with no downhole electrical power. And, because of its location and hook-up, the displacement pump maintains a constant ratio of produced fluid to injected fluid. All of these advantages provide the operational characteristics desired for an effective injection/recovery single well in situ leach mining system.